This invention is directed to a coating composition and in particular to an aqueous coating composition containing an alkyd resin and a polyisocyanate crosslinking agent.
Automotive and truck manufacturers and the automotive and truck repair industry require coating compositions that form finishes that are weatherable, durable, and have an excellent appearance. In particular, the repair industry requires finishes that have excellent adhesion to all types of painted or primed substrates. Manufacturer and repair industry needs have been met by solvent based thermosetting coating compositions such as a coating composition of an alkyd resin and a polyisocyanate as shown by Miller U.S. Pat. No. 3,789,037 issued Jan. 29, 1974 or a solvent based composition of an ambient temperature curing acrylic resin and a polyisocyanate as shown by Miller U.S. Pat. No. 3,844,993 issued Oct. 29, 1974.
Air pollution regulations are becoming stricter in many states and in the future, solvent based coating composition may not be acceptable for use. Water based coating compositions can be used to meet air pollution regulations. Coating compositions containing polyisocyanates are well known crosslinking agents that provide durable finishes. However, to use a polyisocyanate in a water based coating composition, the polyisocyanate is reacted with a blocking agent to prevent isocyanate groups from reacting with water. To cure compositions containing blocked polyisocyanate, elevated temperatures are required to unblock the polyisocyanate. Increased energy costs make coating compositions that require baking, unattractive. Also, many manufacturers and repair shops do not have baking facilities.
The novel coating composition of this invention provides a finish that is acceptable to automotive and truck manufacturers and to the automotive and truck repair industry, meets current pollution regulations and does not require baking at elevated temperatures but cures at ambient temperatures to a durable, weatherable and glossy finish.